This invention relates to a control apparatus for a vehicular generator for use in vehicles, for example, automobiles.
FIG. 1 shows a prior-art control apparatus of the specified type, in which a generator 1 is driven by an engine not shown and is constructed of an armature coil 101 and a field coil 102. A rectifier 2 subjects the A-C outputs of the generator 1 to full-wave rectification, and has output ends 201, 202 and 203. The output end 201 delivers a main output, the output end 202 serves for exciting the field coil 102 and for detecting the voltage of a voltage regulator 3 to be described below, and the output end 203 serves for grounding. The voltage regulator 3 regulates the output voltage of the generator 1 to a predetermined value, and is constructed of components to be mentioned below. Numerals 301 and 302 designate voltage dividing resistors which divide the output voltage of the output end 202 of the rectifier 2, nemeral 303 designates a Zener diode which detects a potential resulting from the voltage division of the voltage dividing resistors 301 and 302 and which is enabled when the potential has reached a predetermined value, and numeral 304 designates a transistor which is turned `on` when the Zener diode 303 is enabled and which controls the on/off action of a transistor 305 to be described below. The transistor 305 interrupts and controls a field current which flows through the field coil 102 of the generator 1. The voltage regulator 3 further includes the base resistor 306 of the transistor 305, and a diode 307 which is connected in parallel with the field coil 102 of the generator 1 and which absorbs the interruption surge of this field coil. Numeral 4 indicates batteries carried on the vehicle, numeral 5 the various electric loads of the vehicle, numeral 6 a key switch, and numeral 7 a resistor for the initial excitation of the field coil 102 of the generator 1. FIG. 2 shows the curves C of the output current of the generator 1 and the curves T of the driving torque thereof versus the rotational speed (revolutions per minute) of the generator 1 under the full-load condition thereof as based on the prior-art apparatus. In this figure, broken lines correspond to a cold condition, and solid lines a hot condition.
In operation, when the key switch 6 is closed in starting the engine (not shown) an initial excitation current flows from the batteries 4 to the field coil 102 of the generator 1 through the key switch 6 as well as the initial excitation resitor 7, whereby the generator 1 is placed in a state capable of generating power. When the engine is subsequently started, the generator 1 begins to generate power. In the voltage regulator 3 which receives the output voltage of the output end 202 of the rectifier 2, when this output voltage exceeds a predetermined value previously set by the voltage dividing resistors 301 and 302 and the Zener diode 303, the Zener diode 303 is enabled to turn `on` the transistor 304. Besides, when the aforementioned output voltage becomes less than the predetermined value, the Zener diode 303 is disabled to turn `off` the transistor 304. The turn-on and -off of the transistor 304 controls the `off` and `on` states of the transistor 305, respectively, and thus interrupts the current of the field coil 102 of the generator 1 so as to regulate the output voltage of the generator 1 to the predetermined value. In this manner, the voltage regulator 3 repeats the above operation to control the state the generator 1 is in, and the generator 1 supplies electric power from the output end 201 of the rectifier 2 to the batteries 4 and various electric loads 5 of the vehicle with the regulated output voltage.
The characteristic curves of the output currents and the driving torques of the generator 1 of the prior-art apparatus controlled as described above, under the cold and hot conditions become as shown in FIG. 2. More specifically, as the generator 1 shifts from the cold state thereof immediately after beginning the power generation, to the hot state thereof in consequence of the self-heating thereof and the rise of an ambient temperature, the output current lowers gradually as seen from the characteristic curve of the cold condition to that of the hot condition as illustrated in FIG. 2. In addition, the nominal output of the generator 1 is determined by the hot condition characteristic, and the cold condition characteristic is merely an allowance for guaranteeing the hot condition characteristic. Ideally, it is considered best that the characteristics under the cold condition and the hot condition be substantially in agreement. On the other hand, the driving torque of the generator 1 lowers gradually from the cold condition characteristic to the hot condition characteristic as the output current lowers. In addition, the driving torque exhibits a peculiar curve which has a peak indicated by a point A in FIG. 2 at a comparatively low speed of rotation.
The driving torque of the generator 1 acts as a load on the engine of the vehicle. Especially in the vicinity of the aforementioned peak at the point A, the engine is at the low speed of rotation and the output torque thereof is comparatively small, so that the driving torque of the generator 1 acts as a very high load.
Since the prior-art control apparatus for the vehicular generator is constructed and operated as described above, the difference between the cold-condition driving torque and the hot-condition driving torque acts as a surplus load on the engine. In particular, immediately after the starting of the engine, the torque generated by the engine is unstable, and the cold-condition driving torque of the generator becomes a large value. Therefore, the degree of influence of the generator driving torque is high to incur the problems that the rotation of the engine is not smooth and becomes unstable, and that the quantity of fuel consumed by the engine becomes large. Further, that the above degree of influence increases at a cryogenic temperature.